1. Field of the Invention
This invention relates to a heavy-duty granular detergent composition capable of preventing eutrophication of river water due to inflow of waste water after washing and also capable of preventing particles from pulverization during the transportation of packaging.
2. Description of the Prior Art
Sodium citrate is known as an effective builder for heavy-duty granular detergents. However, a detergent formulation of this type having a granule strength equal or superior to that of the heavy-type granular detergent comprising sodium tripolyphosphate (STPP) as a builder and having a particle shell strength (i.e. the ultimate strength of a single particle pressed between two parallel surfaces) equal to 4 to 5 g and thus capable of maintaining the spherical granule shape in the course of charging into a container or transport, has not hitherto been known. The product comprising particles of a fairly hollow shape can be produced by spray-drying a slurry containing 5 - 60 wt. percent of sodium citrate prepared by the same process as that of a known detergent containing the same amount of STPP builder. In this case, however, the shell strength of the resulting particle is decidedly inferior as compared to that of the known STPP detergent and amounts only to about 1 to 2 g.
A granular detergent of this type is marketed in the form of a package in a carton, box and the like. If the granule strength of the detergent is low, the detergent granules are apt to be broken into smaller sizes due to heavy vibration caused in the course of handling or transport. Pulverization of a granules so caused results in the decrease of the apparent volume of the granular detergent and detracts from its commercial value. In order to increase the granule strength and to prevent granules from pulverization, the drying capacity is decreased, or sodium tripolyphosphate is added in a larger amount. The former method is however not desirable as it lowers the production efficiency of the granular detergent, and the latter has the deficiency that eutrophication of river water due to inflow of detergent components may be promoted.